[61.05] On the Lack of a Soft X-Ray Excess from Galaxy Clusters

E. J. Lloyd-Davies, J. N. Bregman (University of Michigan)

A soft X-ray excess has been claimed to exist in and around
a number of galaxy clusters and this emission has been
attributed to the warm-hot intergalactic medium that may
constitute most of the baryons in the local universe. We
have examined a study of the XMM-Newton observations by
Kaastra et al. (2003) and find that their X-ray excess (or
deficit) depends upon Galactic latitude and appears to be
related to the surface brightness of the 1/4 keV emission,
generally attributed to the Local hot bubble and the halo of
the Milky Way. We suggest that the presence of the soft
X-ray excess is due to incorrect subtraction of the soft
X-ray background. A re-analysis of the observations, using
backgrounds matched to the 1/4 keV X-ray background and
hydrogen column in the vicinity of the clusters, supports
this hypothesis.